Roger:
The designers of the Caldera stove often write about the integration of the two elements of the kit: the burner and the cone. They point out that they have been designed to work together. In your opinion, would using a different burner such as one of the MiniBull pressurized ones (with the thumb screw seal) or an Elite create a better CO emission signature or develope a more efficient heating rate? I have several of Tinny's stoves and have been wondering about this issue for some time. I also wonder why you did not test one of his sealed burners in your evaluation?

Roger, a very interesting and detailed series of reports. Thanks. However I don't think the carbon monoxide emissions preclude using alcohol stoves in tent vestibules (with some models there are other reasons not to do so such as flaring). In Europe alcohol stoves are often used in tent vestibules, especially by youth groups, as they are regarded as safer than other types of stoves. The models are usually Trangias. I notice you refer to the Trangia as an ancient stove mainly of historic interest. Not in Europe it isn't! Here is still sells well – far better than any gasoline stove. You will see Trangias on the shelves of just about all outdoor shops in the UK. These are the complete Trangias – burner, pots and windshield. This is how the Trangia burner is normally used and I wonder if the results would have been different if you had tested the whole set. I've used the Trangia in a tent vestibule on hundreds of occasions and it has always worked safely if slowly. There is always some ventilation even when the vestibule is closed. More recently I've been testing the Caldera Cone and the White Box Stove and both are much faster at bringing water to the boil than the Trangia though fuel usage is the same.

I got a compressed gas burner for my Trangia 27. In the winter the gas canister can be inverted to make it a very robust winter stove. However you lose simmer control with the canister inverted. It is my favorite 2 person stove because it is so stable and I can make perfect pancakes.

For solo I mostly use the Caldera Cone with 3 cup AGG pot.

Both stoves handle the wind well and are very stable.

The one benefit of ground sleeping is that I can make hot cocoa before I get out of the bag then drink it as I pack and hike before breakfast.

If you want to be popular on nordic ski day trips bring the Trangia 27 and make hot beverages or soup for the group.

I agree with you. Any tent with so little ventilation that CO is a problem probably also has a major condensation problem.

Richard, I have a gas canister burner for the Trangia too. It's so efficient I sometimes worry about melting the windscreen! I mostly use it car camping these days due to the weight. Many years ago when stoves were in general much heavier and there were few canister stoves anyway (and only butane not butane/propane mixes) I used the Trangia with alcohol burner regularly, including on a 10 week walk the length of Britain and mostly in a tent vestibule. I also took it ski touring in Norway. However I must admit the advent of lighter, more efficient canister and gasoline stoves tempted me away from it.

"I notice you refer to the Trangia as an ancient stove mainly of historic interest. Not in Europe it isn't! Here is still sells well – far better than any gasoline stove."

For the record, I would expect that that was also the case in Australia, as there are Trangias and Trangia clones in every outdoor shop and they definitely were (and I would expect they still are) the default stove for all outdoor ed classes, precisely because of their safety. My first stove was a Sigg, which was basically a refined version of the Trangia (duossal pans, simmer ring etc). I really don't understand why Roger thinks that they're only of historical interest in Australia.

I also think that categorising the Trangia burner as a "cat stove" is putting things the wrong way around – the cat stoves are copies of the Trangia, even if only inadvertently.

"These are the complete Trangias – burner, pots and windshield. This is how the Trangia burner is normally used and I wonder if the results would have been different if you had tested the whole set."

I'd have to agree with that. The Trangia system is very sophisticated and works very differently to the home-made meths stove/aluminium foil windscreen system that UL'ers are using. The sum of the Trangia system is very different to the total of the parts.

Because there doesn't seem to have been much history of use of Trangias in the US the differences between how a Trangia works and how a simple home-made meths stove/aluminium foil windscreen system works don't seem to be appreciated by a lot of the UL enthusiasts building cat stoves etc.

For example:

Windscreens

With a home-made meths stove/aluminium foil windscreen system people try to protect the flame.

With a Trangia pointing the "windscreen" vents into the wind actually heats water MORE quickly, not less. This is actually referred to on Trangia's website:

"The ventilation holes in the lower windshield are turned to face into the wind to increase the oxygen supply to the burner. If the wind becomes too strong, the stove is turned to maintain the required flame."

With the greater oxygen supply you'd expect that there might also be less CO.

Starting

I've seen video of cat stoves etc starting up and it's noticeable that the flame does take a while to reach full size. That simply doesn't happen with Trangias – the flame's there at pretty much full strength from the start. I wonder if this is not something to do with the thermal mass of the Trangia burner and that while you can make something like a Trangia burner lighter by using aluminium, by doing so you also reduce its effectiveness. As Trangia say "The Trangia burner is an ingenious original product. Many have tried to copy it, but nobody has completely succeeded."

Cold weather/priming

I've used my Sigg in cold weather and snow camping and I've never needed to use a "priming ring". And what's more, I've never heard of them being used, although I have heard of people warming the burner in their hands or a pocket. Trangia do offer a priming ring (see the page linked to above) but they say it's only for use in "severe cold". I would imagine that for a Swede "severe" cold meant something under -40 C (!!), not temperatures around freezing.

It's noticeable that the two meth stoves that are believed to work the most efficiently – the ThermoJet and the Caldera – both use the Trangia principle, with an enclosed stove and pot fed by air coming through a bottom vent. This system is not a variation of the home-made meths stove/aluminium foil windscreen system, it is qualitatively different.

I have to agree that the Trangia or their clones are still a very popular here in Australia and definitely are the stove of choice with the school outdoor Ed people, in my stove collection I own two trangia’s they are virtually indestructible in twenty years I have only had to replace a lid seal. In OZ I have yet to meet someone with a cat can stove, I mostly see Trangia’s and Whisperlite’s although canister stoves are starting to make an impact. I now prefer canister stoves, my walking partner has just purchased the large pot Jetboil system and I am very impressed with how fast and easy it is to set up and how fast it can boil our water needs although I carry a Pocket Rocket it does not get used much these days.

I gave up using my Trangia for cold weather when one very cold winter day in our local mountains it seemed to take forever and more than one full fuel bowl to boil enough water for two cups of tea. Also alcohol only has about half the specific heating value of canister fuel so more fuel has to be carried and I also like the convenience of easily controlling the flame for simmering.

I admit I'm surprised at the relatively high CO emitted by the cat-style alcohol stoves. Instinctively, I think we all knew going in that butane/prop stoves burned cleanest, and conversely, we thought that kerosene burned dirtiest, follow by white gas. I would have guessed alcohol would have performed considerably closer to butane.

It's hard to imagine that many would opt to use a cat stove in a tent (you can't stop the thing once it's lit) over a butane unit. It turns out Roger's stove preferences are similar to mine, the Kovea (Athena) in winter and the small open red bull for non winter.

The trangia may be ancient to us, but I know of no cat-stoves sold in stores, whereas you can still see trangias in mt. shops, at least here in the rockies.

Eric, here in the UK people regularly use Trangias in tent vestibules (and other stoves – it's standard practice due to our wet and windy weather, along with the midge plague in summer). Many, many years ago I worked summers for an Outward Bound centre in Scotland and students used Trangias in vestibules. The stoves were chosen because they are unpressurised and regarded as safer than canister or gasoline/kerosene models. Before Trangias Primus OO kerosene stoves were used, which were definitely more hazardous in vestibules. As long as a Trangia burner isn't over-filled it won't flare and the windscreen acts as a side barrier to the flames. You can put the flame out by dropping the burner lid over it (remove the rubber seal first!).

I wonder how the CO emissions wood stoves compare to the types tested. Generally, they produce the "long, yellow flames." Based on that, I would suspect them of high CO output. I bring this up because I seem to detect a recent spark (no pun intened) of interest in wood stoves lately.

Um… yeah… unless it's a system specifically designed to exhaust well and contain the flames (aka models similar to kifaru or tigoat) one would be a bit insane to use a woodstove in a tent (or any enclosed area)… however, using them under a tarp may be doable (but not ultralight as the tarp would be in addition to your primary shelter)

At one time Trangias were all over the east coast, since that's where I bought my first one. The problem was finding just the burner, w/o the heavy and expensive cookset.

After dealing with MSR's repair kits, which contained dozens of parts, the Trangia's no parts construction was nice. I don't believe any other alcohol stove let's you quickly snuff it out and store the remaining fuel IN the stove. I believe MSR is or was marketing the Trangia.

Looking at the pictures of the stove that currently come with the Caldera system, it seems as if there may be more holes around the bottom of the stove than there were with the coke-can prototype tested. This might help with oxygen mixing, and may have been intended to address early models' problems at altitude; the distributor says that though early models worked wonderfully at sea level, they were less effective at altitude. The models currently shipping work well at 10,000 feet (and probably higher).

What a great, detailed yet clear, analysis this series of articles has been! Thanks very much.

> The designers of the Caldera stove often write about the integration of the two elements of the kit: the burner and the cone. They point out that they have been designed to work together. In your opinion, would using a different burner such as one of the MiniBull pressurized ones (with the thumb screw seal) or an Elite create a better CO emission signature or develope a more efficient heating rate? I have several of Tinny's stoves and have been wondering about this issue for some time. I also wonder why you did not test one of his sealed burners in your evaluation?

First of all, Will R and I have been working with the Caldera team for some time over their stove system, doing evaluations and giving feedback. So I have some understanding of the system.

As to why I didn't test another stove inside the Caldera Cone – there are three answers.
First, I did not have one of the screw-sealed stoves from Tinny.
Second, I decided to not 'mix systems' at this stage – the combinations would be endless!
Finally, I just plain ran out of time. The article was finished shortly before we (my wife and I) left for France for our multi-month walking trip. Obviously, we have now returned, intact and only suffering slightly…

> I notice you refer to the Trangia as an ancient stove mainly of historic interest. Not in Europe it isn't! Here is still sells well – far better than any gasoline stove. You will see Trangias on the shelves of just about all outdoor shops in the UK.
I looked in every gear shop in every town we went through to see what they had in the way of stoves. Precious little! Gas canisters were often available, and a few shops had Campingaz stoves. I don't think I saw a single Trangia though.

> I wonder if the results would have been different if you had tested the whole set.
I doubt it would solve the problem myself. The problem is as I suggested one of air flow and mixing, and while using the full Trangia kit might improve things slightly, that would probably be the extent of it.
But I don't have a full Trangia kit to test.

This may or may not be a correction, but the article describes "rubbing alcohol" under the section devoted to ethyl alcohols. In the US, the only "rubbing alcohol" which I've seen or used is actually isopropyl, not ethyl. To my knowledge, these bottles have no "denaturing" ingredients, since isopropyl is itself poisonous when ingested (re: MSDS). Though not considered a severe threat in general, 8oz. of pure isopropyl is considered a lethal dose. Methyl is a much bigger threat, especially in regard to skin contact, but drinking isopropyl is certainly not a good idea. Perhaps ethyl is indeed used in some rubbing alcohols, but isopropyl is presently cheaper to manufacture and untaxed, thus generally preferred for use in rubbing alcohol.

It is true that "rubbing alcohol" is up to 30% water, which I suspect is added partly to reduce its desiccative properties. However, isopropyl is commonly available in pure form where I live as a "red bottle" automotive fuel additive. Without added water, isopropyl is a reasonable fuel for some alcohol stoves and theoretically has a higher BTU content by weight than ethyl. In my experience, isopropyl will deposit some soot on your pot, so it is not as clean-burning as ethyl. I consider it much safer and overall a "better" fuel choice than methyl and thus recommend it if no denatured alcohol is available. As Roger points out, though, actual "rubbing" alcohol with water added is completely useless as it will not burn hotly.

By the way, in this article Roger seems to ask why it's called "rubbing" alcohol. Well, next time you get a shot in the arm (or elsewhere), that cotton pad they use to sanitize and slightly anesthetize the area is traditionally soaked in rubbing alcohol. They rub it over the area before shoving a needle in you, thus the name. At least that's my perspective.

Using a different burner in the caldera cone is chancy. The heat level inside the Cone is much higher, and this could do bad things to a pressurised stove. Maybe. It would depend very much on the particular case.

There is not a lot of difference in practice between a 'sealed' stove and something like the Elite, which I did test. Both are pressurised.

> This is how the Trangia burner is normally used and I wonder if the results would have been different if you had tested the whole set.

I don't think the results would be all that different. What matters is how much oxygen gets mixed in with the alcohol vapour, once the vapour has come out of the small holes. All the full Trangia kit could do normally would be to reduce the amount of oxygen available.

In answer to your specific question…..yes….we ran many different burner designs inside the cone in our attempts to find what worked best as we were developing the Caldera system.

The worst performing design is the pressure/jetted variation. It burns very hot and very fast. Because of that, we saw two different symptoms inside the cone. The most prominent was, as Roger mentioned, that it got way too hot inside. Since we are capturing all that heat, the effect was to boil off the alcohol very fast, making it even hotter, which captured even more heat which boiled it off even faster….in essence sending it into a runaway condition that was horribly inefficient and damaged the cone. The other, less common condition we saw with pressure stoves was that they very quickly burned up all the oxygen….choking them out….then sputtering back to life…burning up more oxygen that choked them out….etc.

The open burner is the only one that really stands a chance inside that environment. Even with this, we had to go through a ton of different design modifications in order to narrow down to the right venting and geometry that worked predictably, efficiently, and consistently across a reasonable range of altitudes. Again, Roger and Will were a tremendous asset in helping us narrow this down as they hauled our early designs into very inhospitable climes.

So, this is the reason we always insist on sending our stove along with each cone. While there might be one or two other commercial designs around that could work, we really don't have the ability to qualify them all or keep up with their designs as they evolve. Quantifying and bounding the DIY products would be next to impossible.

I want to confirm Rand's observations. I own a Caldera stove and have used it, and once tried it with a different brand stove and sure enuf, it softened part of the Windscreen (made it bend and char). Use their stove with their windscreen, and by the way, the combo gives you the best burn, most efficient use of alchol, requiring the least burned amount to boil. Also, it works so great in high wind and is such a great pot stabilizer too. I can't say enuf good things about it, it's that good.